Forensic Study of Warranty Project on US82

Abstract

This forensic study is unique in that it involves a pavement warranty specification. Extensive field and laboratory testing was conducted to determine the cause(s) of longitudinal cracks observed on the surface. Four trenches were cut and removed to allow more testing on top of each pavement layer. The tests found that the stiffness of the foamed asphalt base is higher than that of a typical flexible base. However, the subgrade modulus is low compared with the average subgrade modulus in Texas. Water seeped into two trenches (dug into the road where there were surface cracks) within 20 min of digging. No water was observed in the other two trenches, where there were no surface cracks. The two trenches with surface cracks have lower base density and higher base moisture content than the two with no surface cracks. Based on observations of the trenching and coring operations, the same surface cracks have been detected in the base layer. Cracks up to 150 mm into the base layer have been observed. Although cracks have been observed in the base (and they can be related to lower stiffness and higher falling weight deflectometer deflections), it is difficult to determine if the cause of surface cracks is due to the base layer alone. It is difficult to prove if the layer is responsible for the failure, except by properties listed in the specification. One faulty pavement layer can easily cause the failure of other layers. For warranty purposes, layer-specific failure criteria should be clearly outlined. The base did not meet the gradation specification. The field material was substantially finer than specified. While some specifications may have been violated, there is little evidence to show that the cause of the longitudinal cracking is primarily related to the foamed-asphalt-stabilized base.